Illuminating lens, lighting device, surface light source, and liquid-crystal display apparatus

ABSTRACT

A light exit surface of an illuminating lens has a first light exit surface and a second light exit surface. The first light exit surface is recessed toward a point on the optical axis, and the second light exit surface extends outwardly from the periphery of the first light exit surface. The first light exit surface has a transmissive region and a total reflection region. When the position of a light source on the optical axis is defined as a starting point, the transmissive region transmits light that has been emitted from the starting point at a relatively small angle with respect to the optical axis, and the total reflection region totally reflects light that has been emitted from the starting point at a relatively large angle with respect to the optical axis. A bottom surface that surrounds a light entrance surface and faces oppositely to the light exit surface is provided with a projecting portion or a recessed portion for reflecting light that has been emitted from the light source, totally reflected repeatedly at the light exit surface, and then reached the bottom surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illuminating lens for widening a range of transmission directions for light from a light source such as a light emitting diode, and to a lighting device using this illuminating lens. The present invention further relates to a surface light source including a plurality of lighting devices, and to a liquid-crystal display apparatus in which this surface light source is disposed behind a liquid-crystal panel to serve as a backlight.

2. Description of Related Art

In a conventional backlight of a large-sized liquid-crystal display apparatus, a number of cold cathode tubes are disposed immediately below a liquid-crystal panel, and these cold cathode tubes are used with other members such as a diffusing plate and a reflecting plate. In recent years, light emitting diodes have been used as light sources for backlights. Light emitting diodes have increased their efficiency recently, and are expected to serve as low-power light sources to replace fluorescent lamps. In the case where light emitting diodes are used as a light source in a liquid-crystal display apparatus, the power consumption of the apparatus can be reduced by controlling the light and dark states of the light emitting diodes according to an image to be displayed.

In a backlight of a liquid-crystal display apparatus using light emitting diodes as a light source, a large number of light emitting diodes are disposed therein instead of cold cathode tubes. The use of a large number of light emitting diodes allows the entire surface of the backlight to have uniform brightness, but the need for such a large number of light emitting diodes is an obstacle to cost reduction. In view of this, attempts to increase the output power of each light emitting diode to reduce the required number of light emitting diodes have been made. For example, Japanese Patent No. 3875247 has proposed a lens that is designed to provide a uniform surface light source with a reduced number of light emitting diodes.

In order to obtain a uniform surface light source with a reduced number of light emitting diodes, the area to be irradiated with the light emitted from each light emitting diode needs to be increased. That is, light emitted from each light emitting diode needs to be spread to obtain a wider range of transmission directions for light from the diode. For this purpose, in Japanese Patent No. 3875247, a lens having a circular shape in a plan view is disposed on a light emitting diode as a chip to control the directivity of the chip. The light exit surface of this lens, through which light exits the lens, has a shape such that a portion in the vicinity of the optical axis is a concave and a portion surrounding the concave is a convex extending continuously from the concave.

On the other hand, JP 2008-305923 A has proposed a lens that is designed to provide a more uniform surface light source. In this lens, light that has been Fresnel reflected at the light exit surface of the lens back to the light entrance surface side thereof is reflected again by total reflection to be guided toward the surface to be irradiated.

A light emitting diode as a chip emits light mostly in the front direction of the light emitting diode chip. In the lens disclosed in Japanese Patent No. 3875247, light that has been emitted in the front direction of the chip is refracted at the concave surface in the vicinity of the optical axis and diffused. As a result, the surface to be irradiated is illuminated to have a wide illuminance distribution with a reduced illuminance in the vicinity of the optical axis.

In the lens disclosed in Japanese Patent No. 3875247, however, the light emitted from the light source needs to be refracted, and therefore the difference in height between the concave and the convex must be reduced to a certain level. That is, there is a limit to a widening of the range of transmission directions for light from the light source. The lens disclosed in JP 2008-305923 A has the same limit because it is designed to distribute the light emitted from the chip by utilizing the refraction of the light.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an illuminating lens capable of further widening the range of transmission directions for light from a light source, and to provide a lighting device, a surface light source, and a liquid-crystal display apparatus each including this illuminating lens.

In order to achieve the above object, the present inventors have considered it important, in obtaining a wider range of transmission directions for light from a light source, to distribute radially the intense light that has been emitted in the front direction of the light emitting diode chip, and come up with an idea of distributing radially the light emitted in the front direction of the light emitting diode chip by utilizing intentionally the total reflection of the light. Accordingly, the present inventors have conceived an illuminating lens described below.

That is, the illuminating lens is a lens for spreading light emitted from a light source so that a surface to be irradiated is irradiated with the spread light, and includes: a light entrance surface through which the light emitted from the light source enters the lens; and a light exit surface through which the light that has entered the lens exits the lens. The light exit surface has a first light exit surface and a second light exit surface. The first light exit surface is recessed toward a point on an optical axis of the illuminating lens, and the second light exit surface extends outwardly from a periphery of the first light exit surface to form a convex. The first light exit surface has a transmissive region located in the center of the first light exit surface and a total reflection region located around the transmissive region. When the position of the light source on the optical axis is defined as a starting point, the transmissive region transmits light that has been emitted from the starting point at a relatively small angle with respect to the optical axis and then reached the first light exit surface, and the total reflection region totally reflects light that has been emitted from the starting point at a relatively large angle with respect to the optical axis and then reached the first light exit surface. The second light exit surface has a shape capable of transmitting approximately the entire amount of light that has been emitted from the starting point and then reached the second light exit surface.

In the illuminating lens configured as described above, the range of transmission directions for light from the light source can be widened more by utilizing positively the total reflection of light. As shown in FIG. 28, in this illuminating lens, the light is totally reflected at the total reflection region of the first light exit surface in the light exit surface 112. Then, a part of the light again is totally reflected repeatedly at the second light exit surface extending outwardly from the first light exit surface, and reaches the bottom surface 113 that surrounds the light entrance surface 111 and faces oppositely to the light exit surface 112. The light that has reached the bottom surface 113 passes through the bottom surface 113, and then is reflected at the member 130 (for example, a substrate) that faces the bottom surface 113 to be guided toward the surface to be irradiated. In this case, the position on the surface to be irradiated reached by the light reflected from the member 130 is determined by the clearance between the bottom surface 113 and the member 130, but the cost for maintaining the clearance with a high degree of accuracy is high. For this reason, it is desired that the illuminance on the surface to be irradiated be stabilized with a lower cost configuration. The present invention has been made in view of the above circumstances.

The present invention provides an illuminating lens for spreading light emitted from a light source so that a surface to be irradiated is irradiated with the spread light. The lens includes: a light entrance surface through which the light emitted from the light source enters the lens; a light exit surface through which the light that has entered the lens exits the lens; and a bottom surface configured to surround the light entrance surface and to face oppositely to the light exit surface. In this illuminating lens, the light exit surface has a first light exit surface and a second light exit surface. The first light exit surface is recessed toward a point on an optical axis of the illuminating lens, and the second light exit surface extends outwardly from a periphery of the first light exit surface to form a convex. The first light exit surface has a transmissive region located in the center of the first light exit surface and a total reflection region located around the transmissive region. The transmissive region transmits light that has been emitted from a starting point at a relatively small angle with respect to the optical axis and then reached the first light exit surface, when a position of the light source on the optical axis is defined as the starting point. The total reflection region totally reflects light that has been emitted from the starting point at a relatively large angle with respect to the optical axis and then reached the first light exit surface. The second light exit surface has a shape capable of transmitting approximately the entire amount of light that has been emitted from the starting point and then reached the second light exit surface, and of totally reflecting approximately the entire amount of the light that has been totally reflected at the total reflection region and then reached the second light exit surface. The bottom surface is provided with a projecting portion or a recessed portion for reflecting light that has been emitted from the light source, totally reflected repeatedly at the light exit surface, and then reached the bottom surface. The projecting portion or the recessed portion has a pair of side surfaces that meet each other to form a ridge.

Herein, “approximately the entire amount” means at least 90% of the entire amount. It may be the entire amount, and may be an amount slightly smaller than the entire amount.

The present invention also provides a lighting device including: a light emitting diode for emitting light; and an illuminating lens for spreading light emitted from the light emitting diode so that a surface to be irradiated is irradiated with the spread light. This illuminating lens is the above-mentioned illuminating lens.

The present invention further provides a surface light source including: a plurality of lighting devices arranged in a plane; and a diffusing plate disposed to cover the plurality of lighting devices, and configured to receive on one surface thereof light emitted from the plurality of lighting devices and to emit the light from the other surface thereof in a diffused manner. Each of the plurality of lighting devices is the above-mentioned lighting device.

The present invention still further provides a liquid-crystal display apparatus including: a liquid-crystal panel; and the above-mentioned surface light source disposed behind the liquid-crystal panel.

According to the present invention, it is possible not only to obtain a wider range of transmission directions for light from the light source but also to stabilize the illuminance of the surface to be irradiated with a low cost configuration in which the bottom surface is provided with a projecting portion or a recessed portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illuminating lens according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of the main portions of FIG. 1.

FIG. 3 is a schematic diagram of a lighting device according to a second embodiment of the present invention.

FIG. 4 is a diagram showing optical paths of light rays that reach a transmissive region of a first light exit surface of the lighting device according to the second embodiment of the present invention.

FIG. 5 is a diagram showing optical paths of light rays that reach a total reflection region of a first light exit surface of the lighting device according to the second embodiment of the present invention.

FIG. 6 is a diagram showing optical paths of light rays that exist the lighting device through a second light exit surface thereof according to the second embodiment of the present invention.

FIG. 7 is a diagram for explaining Example 1 of the lighting device according to the second embodiment of the present invention.

FIG. 8 is a diagram for explaining Examples 2 and 3 of the lighting device according to the second embodiment of the present invention.

FIG. 9 is a graph showing a relationship between θi and sagY, which represent the shape of the light exit surface in Example 1 of the lighting device according to the second embodiment of the present invention (i.e., a graph obtained by plotting the values in Table 1).

FIG. 10 is a graph showing a relationship between θi and sagY, which represent the shape of the light exit surface in Example 2 of the lighting device according to the second embodiment of the present invention (i.e., a graph obtained by plotting the values in Table 2).

FIG. 11 is a graph showing a relationship between θi and sagY, which represent the shape of the light exit surface in Example 3 of the lighting device according to the second embodiment of the present invention (i.e., a graph obtained by plotting the values in Table 3).

FIG. 12 is a graph showing a relationship between r/R and θi-θn in Example 1 of the lighting device according to the second embodiment of the present invention.

FIG. 13 is a graph showing a relationship between r/R and θi-θn in Example 2 of the lighting device according to the second embodiment of the present invention.

FIG. 14 is a graph showing a relationship between r/R and θi-θn in Example 3 of the lighting device according to the second embodiment of the present invention.

FIG. 15 shows an illuminance distribution in Example 1 of the lighting device according to the second embodiment of the present invention.

FIG. 16 shows an illuminance distribution in Example 2 of the lighting device according to the second embodiment of the present invention.

FIG. 17 shows an illuminance distribution in Example 3 of the lighting device according to the second embodiment of the present invention.

FIG. 18 shows an illuminance distribution obtained when only light emitting diodes are used to confirm the effects of Examples 1 to 3.

FIG. 19 is a schematic diagram of a surface light source according to a third embodiment of the present invention.

FIG. 20 is a partial cross-sectional view of the surface light source according to the third embodiment of the present invention.

FIG. 21 shows an illuminance distribution obtained when the lighting device of Example 1 is used in the surface light source according to the third embodiment of the present invention.

FIG. 22 shows an illuminance distribution obtained when the lighting device of Example 2 is used in the surface light source according to the third embodiment of the present invention.

FIG. 23 shows an illuminance distribution obtained when the lighting device of Example 3 is used in the surface light source according to the third embodiment of the present invention.

FIG. 24 shows an illuminance distribution obtained when a surface light source including lighting devices each composed of only a light emitting diode is used to confirm the effects of Examples 1 to 3.

FIG. 25 is a schematic diagram of a liquid-crystal display apparatus according to a fourth embodiment of the present invention.

FIG. 26 is a plan view of a modified illuminating lens.

FIG. 27A and FIG. 27B are each a plan view of an illuminating lens of another embodiment.

FIG. 28 is a schematic diagram of an illuminating lens that has been conceived before.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

An illuminating lens according to the first embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of an illuminating lens 1 according to the first embodiment. The illuminating lens 1, which is disposed between a light source (not shown in FIG. 1) having directivity and a surface to be irradiated 3, spreads light emitted from the light source and emits the spread light to the surface to be irradiated 3. That is, the illuminating lens 1 widens the range of transmission directions for light from the light source. In the illuminance distribution on the surface to be irradiated 3, the illuminance is greatest on the optical axis A that is the design center line of the illuminating lens 1 and decreases almost monotonically toward the edge. The light source and the illuminating lens 1 are disposed so that their optical axes coincide with each other.

Specifically, the illuminating lens 1 has a light entrance surface 11 through which the light emitted from the light source enters the lens and a light exit surface 12 through which the light that has entered the lens exits the lens. The illuminating lens 1 has a bottom surface 13 surrounding the light entrance surface 11 and facing oppositely to the light exit surface 12. Furthermore, in the present embodiment, a radially outwardly projecting ring portion 15 is provided between the light exit surface 12 and the bottom surface 13. The periphery of the light exit surface 12 is joined to the outer edge of the bottom surface 13 via the outer surface of the ring portion 15 having an approximately U-shaped cross section. The ring portion 15 may be omitted. In this case, the periphery of the light exit surface 12 may be joined to the outer edge of the bottom surface 13 with an end face having a straight or arcuate cross section.

In the present embodiment, the light exit surface 12 is axisymmetric with respect to the optical axis A. The contour of the illuminating lens 1 in plan view need not be axisymmetric with respect to the optical axis A. For example, as shown in FIG. 26, the illuminating lens 1 may have an oval shape, in which the ring portion 15 has a pair of flat portions 15 a that are parallel to each other across the optical axis A, when viewed from the optical axis direction.

The light entrance surface 11 need not be axisymmetric with respect to the optical axis A. In the present embodiment, the region that is connected optically to the light source is the light entrance surface 11. Preferably, the annular bottom surface 13 surrounding the light entrance surface 11 is flat. In FIG. 1, the light entrance surface 11 and the bottom surface 13 are on the same level, but there may be a level difference between the light entrance surface 11 and the bottom surface 13. For example, the illuminating lens 1 may be configured such that the light entrance surface 11 is located closer to the light exit surface 12 than the bottom surface 13 and the light source is fitted in the recess formed by the level difference between the surfaces 11 and 13. The light entrance surface 11 need not necessarily be joined directly to the light source. For example, the light entrance surface 11 may be recessed in a hemispherical shape so that an air space is formed between the light entrance surface 11 and the light source.

The light emitted from the light source enters the illuminating lens 1 through the light entrance surface 11, exits the lens 1 through the light exit surface 12, and then reaches the surface to be irradiated 3. The light emitted from the light source is spread by the action of the light exit surface 12, and reaches a large area of the surface to be irradiated 3.

As the light source, for example, a light emitting diode can be used. Light emitting diodes usually are chips with a rectangular plate shape. Therefore, it is preferable that the light entrance surface 11 of the illuminating lens 1 have a shape conforming to the shape of a light emitting diode to fit in close contact with the light emitting diode. The light emitting diode is in contact with the light entrance surface 11 of the illuminating lens 1 via a bonding agent, and connected optically to the light entrance surface 11. The light emitting diode usually is covered with a sealing resin to avoid contact with air. As a conventional sealing resin for a light emitting diode, an epoxy resin, silicone rubber, or the like is used.

The illuminating lens 1 is made of a transparent material having a specified refractive index. The refractive index of the transparent material is, for example, about 1.4 to 1.5. Examples of such a transparent material include resins such as epoxy resin, silicone resin, acrylic resin, and polycarbonate, and rubbers such as silicone rubber. Particularly, it is preferable to use epoxy resin, silicone rubber, or the like that has been used as a sealing resin for a light emitting diode.

The light exit surface 12 includes a first light exit surface 121 that is recessed toward a point on the optical axis A, and a second light exit surface 122 extending radially outwardly from the periphery of the first light exit surface 121 to form a convex. Light enters the illuminating lens 1 through the light entrance surface 11 at a wide range of angles. Light that has entered the lens at a small angle with respect to the optical axis A reaches the first light exit surface 121, and light that has entered the lens at a larger angle with respect to the optical axis A reaches the second light exit surface 122.

Next, the shapes of the first light exit surface 121 and the second light exit surface 122 will be described. For that purpose, a starting point Q is defined first, and then light emitted from the starting point Q is assumed. As stated herein, the starting point Q is the position of the light source on the optical axis A. In the case where a light emitting diode is used as a light source, the starting point Q is the point of intersection of the optical axis A and the light emitting surface that is the front surface of the light emitting diode. That is, the starting point Q is spaced from the light entrance surface 11 by the thickness of the above-mentioned bonding agent. When an angle between the optical axis A and a line connecting the starting point Q and the boundary between the first light exit surface 121 and the second light exit surface 122 is θb, light that has been emitted from the starting point Q at an angle reaches the first light exit surface 121 or the second light exit surface 122 based on the angle θb as a threshold angle.

As shown in FIG. 2, the first light exit surface 121 includes a transmissive region 123 located in the center of the first light exit surface 121 and a total reflection region 124 located around the transmissive region 123. The transmissive region 123 transmits light that has been emitted from the starting point Q at a relatively small angle of less than a specified value θp with respect to the optical axis A and reached the first light exit surface 121, and the total reflection region 124 totally reflects light that has been emitted from the starting point Q at a relatively large angle of θp or more with respect to the optical axis A and reached the first light exit surface 121. That is, θp is an angle between the optical axis A and a line connecting a point P and the starting point Q, when the point P is a point on the boundary between the transparent region 123 and the total reflection region 124.

On the other hand, the second light exit surface 122 has a shape capable of transmitting approximately the entire amount of light that has been emitted from the starting point Q and reached the second light exit surface 122, and totally reflecting approximately the entire amount of the light that has been totally reflected at the total reflection region 124 and reached the second light exit surface 122. The angle between the optical axis A and the light emitted from the starting point Q increases toward the outer edge of the second light exit surface 122. The angle of the light emitted from the starting point Q with respect to a normal line at the point on the second light exit surface 122 reached by the emitted light is the incident angle of the light with respect to the second light exit surface 122. An excessively large incident angle causes total reflection. The incident angle needs to be kept small in order to prevent total reflection. Accordingly, the second light exit surface 122 has a shape such that the angle between the normal line and the optical axis A increases with increasing distance from the optical axis A. That is, the shape of the second light exit surface 122 is a convex.

The entire second light exit surface 122 need not necessarily transmit the light emitted from the starting point Q (i.e., the second light exit surface 122 need not transmit the entire amount of the light). The second light exit surface 122 may have a shape capable of totally reflecting a part of the light emitted from the starting point Q and transmitting the remaining part of the light.

Furthermore, in the present embodiment, the bottom surface 13 is provided with a projecting portion 10 having a ring shape with the optical axis A being the center thereof, as shown in FIG. 1. For more detail, the projecting portion 10 has a pair of side surfaces 10 a and 10 b that meet each other to form a ridge. One or both of the pair of side surfaces 10 a and 10 b may be curved surfaces having an arc-shaped cross section, but preferably both of the side surfaces are tapered surfaces having a straight-line cross section. The same applies to the case where the recessed portion 10′ is formed instead of the projecting portion 10, as to be described later.

The light emitted from the light source is totally reflected at the total reflection region 124 of the first light exit surface 121 and then reaches the second light exit surface 122 (see FIG. 5). A part of the light that has reached the second light exit surface 122 passes through the second light exit surface 122, but most of the remaining part of the light is totally reflected one or more times again at the second light exit surface 122. The light travels along the second light exit surface 122 while being totally reflected one or more times again at the second light exit surface 122, and then reaches the bottom surface 13. The most part of the light that has thus reached the bottom surface 13 is totally reflected at one of the side surfaces 10 a and 10 b of the projecting portion 10 and then totally reflected again at the other side surface to change the traveling direction. As a result, the light travels along the optical path in the lens toward the light exit surface 12. That is, the projecting portion 10 is provided for reflecting the light that has been totally reflected repeatedly at the light exit surface 12 (i.e., the total reflection region 124 of the first light exit surface 121 and the second light exit surface 122) and then reached the bottom surface 13.

In the illuminating lens 1 configured as described above, the most part of the light that has been emitted from the light source and reached the transmissive region 123 located in the center of the first light exit surface 121 is refracted at the transmissive region 123, and thus the area surrounding the optical axis A of the lens on the surface to be irradiated 3 is irradiated with the refracted light. On the other hand, the most part of the light that has been emitted from the light source and reached the total reflection region 124 located on the peripheral side of the first light exit surface 121 is totally reflected at the total reflection region 124. The most part of the totally reflected light reaches the bottom surface 13, is reflected at the side surfaces 10 a and 10 b of the projecting portion 10, and then the surface to be irradiated 3 is irradiated with the reflected light. Furthermore, the most part of the light that has been emitted from the light source and reached the second light exit surface 122 is refracted at the second light exit surface 122, and thus the area away from the optical axis A of the lens on the surface to be irradiated 3 is irradiated with the refracted light. Accordingly, the illuminating lens 1 of the present embodiment allows the range of transmission directions for light from the light source to be widened further. Therefore, the outer diameter of the lens of the present embodiment may be smaller than that of a conventional lens having a concave for only refracting light.

Furthermore, in the present embodiment, the light that has reached the bottom surface 13 can be guided definitely toward the surface to be irradiated 3 with a low cost configuration in which the bottom surface 13 is provided with the projecting portion 10. As a result, the illuminance of the surface to be irradiated 3 can be stabilized. Furthermore, the amount of light directed toward the optical axis A of the lens on the surface to be irradiated 3 can be adjusted by choosing a suitable shape of the projecting portion 10.

Alternatively, instead of the projecting portion 10, a recessed portion 10′ having a ring shape with the optical axis A being the center thereof may be formed, as shown in FIG. 8. The recessed portion 10′ having a pair of side surfaces 10 a and 10 b that meet each other to form a ridge also produces the same effect as the projecting portion 10. In the case where the recessed portion 10′ is formed, however, the light that has reached the bottom surface 13 is totally reflected at only one of the side surfaces 10 a and 10 b of the recessed portion 10′.

The basic configuration of the illuminating lens 1 of the present embodiment has been described so far. A preferable configuration of the illuminating lens 1 of the present embodiment will be described below.

Preferably, the projecting portion 10 or the recessed portion 10′ satisfies the following inequalities (1) to (3).

0.1<R _(in) /R<0.75  (1)

0.75<R _(out) /R  (2)

0.62<(R _(out) +R _(T))/2R<0.95  (3)

where R_(in) is an internal radius of the projecting portion or the recessed portion, R_(out) is an outer radius of the projecting portion or the recessed portion, R_(T) is a distance between the optical axis and the ridge formed by the pair of side surfaces of the projecting portion or the recessed portion that meet each other, and R is an outermost radius of the illuminating lens.

These inequalities (1) to (3) define the proportion of the area of the projecting portion 10 or the recessed portion 10′ on the bottom surface 13, and indicate the range of proportions for controlling suitably the amount of light directed to the surface to be irradiated 3. As for the inequality (1), when the value of R_(in)/R is 0.1 or less, the projecting portion or the recessed portion intrudes between the lens and the light source. In such a case, air enters the space between the lens and the light source and good optical contact cannot be obtained, or the lens is decentered when they are attached, which causes an uneven illuminance. When R_(in)/R is 0.75 or more, the light that has been reflected at the bottom surface tends to be converged toward the optical axis on the surface to be irradiated, which causes an uneven illuminance easily. As for the inequality (2), when R_(out)/R is 0.75 or less, the light that has been reflected at the bottom surface tends to be converged toward the optical axis on the surface to be irradiated, which causes an uneven illuminance easily. As for the inequality (3), when (R_(out)+R_(T))/2R is 0.95 or more, the space between the outermost periphery of the lens and the outer edge of the projecting portion or the recessed portion is too small, which causes reduced workability. When (R_(out)+R_(T))/2R is 0.62 or less, the light that has been reflected at the bottom surface tends to be converged toward the optical axis on the surface to be irradiated, which causes an uneven illuminance easily.

In the case where the bottom surface 13 is provided with the projecting portion 10, the projecting portion 10 preferably satisfies the following inequality (4). On the other hand, in the case where the bottom surface 13 is provided with the recessed portion 10′, the recessed portion 10′ preferably satisfies the following inequality (5).

5.0 degrees<tan⁻¹(h/(R _(out) −R _(T)))<50.0 degrees  (4)

15.0 degrees<tan⁻¹(h/(R _(out) −R _(T)))<30.0 degrees  (5)

where h is a height from the bottom surface to the ridge formed by the pair of side surfaces of the projecting portion that meet each other, or a depth from the bottom surface to the ridge formed by the pair of side surfaces of the recessed portion that meet each other.

These inequalities (4) and (5) define the inclination of the outer side surface 10 b of the projecting portion 10 or the recessed portion 10′, and indicate the range of inclinations of the outer side surface (i.e., a reflective surface) 10 b. As for the inequality (4), when tan⁻¹(h/(R_(out)−R_(T))) is 5.0 degrees or less, the light that has been reflected at the bottom surface is hardly affected by the reflection at the outer side surface of the projecting portion. When tan⁻¹(h/(R_(out)−R_(T))) is 50.0 degrees or more, the light that has been reflected at the outer side surface of the projecting portion is converged toward the optical axis again, which causes an uneven illuminance. As for the inequality (5), when tan⁻¹(h/(R_(out)−R_(T))) is 15.0 degrees or less, the light that has been reflected at the bottom surface hardly is affected by the reflection at the outer side surface of the recessed portion. When tan⁻¹(h/(R_(out)−R_(T))) is 30.0 degrees or more, the light that has been reflected at the outer side surface of the recessed portion is converged toward the optical axis again, which causes an uneven illuminance.

The illuminating lens of the present invention also is applicable to light sources (such as lasers and organic ELs) as well as light emitting diodes.

In the present embodiment, the light exit surface 12 is axisymmetric with respect to the optical axis A. The light exit surface 12, however, need not be axisymmetric with respect to the optical axis A. For example, as shown in FIG. 27A, the light exit surface 12 may have an elliptical shape when viewed from the optical axis direction. This illuminating lens 1 is suitable particularly for an elongated light source. Alternatively, as shown in FIG. 27B, the light exit surface 12 may have a rounded rectangular shape when viewed from the optical axis direction.

Second Embodiment

FIG. 3 is a schematic diagram of a lighting device 7 according to a second embodiment of the present invention. This lighting device 7 includes a light emitting diode 2 for emitting light, and an illuminating lens 1 of the first embodiment for spreading light emitted from the light emitting diode 2 so that the surface to be irradiated 3 is irradiated with the spread light.

The light emitting diode 2 is in contact with the light entrance surface 11 of the illuminating lens 1 via a bonding agent, and connected optically to the light entrance surface 11. The light that has exited the illuminating lens 1 through the light exit surface 12 reaches the surface to be irradiated 3, and thus the surface to be irradiated 3 is illuminated with that light.

Light generation in the light emitting diode 2 has no directivity in itself, and a light emitting region has a refractive index of at least 2.0. When light from the light emitting region enters a low refractive region, the refraction of the light at the interface causes the light to have the maximum intensity in the normal direction of the interface and to have a lower intensity as the angle of the light with respect to the normal line increases. As described above, since the light emitting diode 2 has high directivity, it is necessary to widen the range of transmission directions for light therefrom using the illuminating lens 1 to illuminate a larger area.

FIG. 4 is a diagram showing the paths of light rays in the lighting device 7. In FIG. 4, the paths of light rays that are emitted from the light source at small angles and reach the transmissive region 123 (see FIG. 2) of the first light exit surface 121 are described. The light that has been emitted from the light emitting diode 2 passes through the light entrance surface 11 and reaches the transmissive region 123 of the first light exit surface 121. The light that has reached the transmissive region 123 of the first light exit surface 121 passes through the transmissive region 123 while being refracted, and then reaches the surface to be irradiated 3.

FIG. 5 is a diagram showing the paths of light rays in the lighting device 7. In FIG. 5, the paths of light rays that are emitted from the light source at small angles and reach the total reflection region 124 (see FIG. 2) of the first light exit surface 121 are described. The light that has been emitted from the light emitting diode 2 passes through the light entrance surface 11 and reaches the total reflection region 124 of the first light exit surface 121. The light that has reached the total reflection region 124 of the first light exit surface 121 is totally reflected at the total reflection region 124. The light that has traveled near the optical axis A is totally reflected to reach the second light exit surface 122, and then passes through the second light exit surface 122 while being refracted. In the case where a reflecting plate is provided on the side of the light entrance surface 11 of the illuminating lens 1, approximately the entire amount of light that has passed through the second light exit surface 122 reaches the surface to be irradiated 3. On the other hand, the light that has traveled away from the optical axis A is totally reflected to reach the second light exit surface 122, and then totally reflected at the second light exit surface 122 one or more times and reaches the bottom surface 13. Then, the light is reflected at the projecting portion 10, passes through the light exit surface 12 while being refracted, and then reaches the surface to be irradiated 3.

FIG. 6 is a diagram showing the paths of light rays in the lighting device 7. In FIG. 6, the paths of light rays that are emitted from the light source at larger angles and reach the second light exit surface 122 are described. The light that has been emitted from the light emitting diode 2 passes through the light entrance surface 11 and reaches the second light exit surface 122. In the case where the second light exit surface 122 does not have a shape capable of totally reflecting a part of the light, approximately the entire amount of the light that has reached the second light exit surface 122 passes through the second light exit surface 122 while being refracted, and then reaches the surface to be irradiated 3.

Hereinafter, Examples 1 to 3 are given as specific numerical examples of the present invention.

FIG. 7 is a schematic diagram of a lighting device in Example 1 according to the second embodiment of the present invention. FIG. 8 is a schematic diagram of lighting devices in Examples 2 and 3 according to the second embodiment of the present invention. Examples 1 to 3 are examples of a lighting device designed to widen the range of transmission directions for light from a 0.8 mm cubic-shaped light emitting diode as a light source. In FIG. 7 and FIG. 8, θi is an angle between the optical axis A and a straight line connecting the position of the light source (starting point Q) on the optical axis A and an arbitrary point on the light exit surface 12. In FIG. 7 and FIG. 8, θn is an angle between the optical axis A and a normal line at the arbitrary point on the light exit surface 12, that is, a normal line at a position on the light exit surface 12 reached by the light that has been emitted from the light source position (starting point Q) on the optical axis A at an angle of θi. Furthermore, in FIG. 7 and FIG. 8, sagY is a distance along the optical axis A between the light source position (starting point Q) on the optical axis A and the arbitrary point on the light exit surface 12.

Example 1

Table 1 below shows specific numerical values in Example 1.

TABLE 1 θi sagY 0.000 1.942 0.634 1.944 1.264 1.949 1.888 1.957 2.502 1.968 3.104 1.983 3.692 1.999 4.265 2.018 4.823 2.039 5.364 2.061 5.889 2.085 6.397 2.109 6.890 2.135 7.368 2.162 7.831 2.189 8.280 2.216 8.717 2.244 9.141 2.271 9.554 2.299 9.957 2.327 10.349 2.355 10.733 2.382 11.108 2.409 11.475 2.436 11.835 2.462 12.189 2.488 12.537 2.514 12.879 2.539 13.216 2.563 13.548 2.587 13.877 2.611 14.201 2.634 14.522 2.656 14.840 2.678 15.155 2.699 15.467 2.720 15.777 2.739 16.085 2.759 16.391 2.778 16.695 2.796 16.997 2.813 17.298 2.830 17.598 2.847 17.897 2.863 18.194 2.878 18.491 2.893 18.787 2.907 19.081 2.921 19.375 2.935 19.669 2.947 19.961 2.960 20.253 2.972 20.544 2.983 20.835 2.994 21.125 3.005 21.414 3.015 21.702 3.025 21.990 3.035 22.277 3.044 22.563 3.053 22.849 3.062 23.133 3.070 23.417 3.078 23.699 3.086 23.981 3.093 24.261 3.101 24.541 3.108 24.819 3.115 25.096 3.122 25.372 3.128 25.646 3.135 25.919 3.141 26.190 3.147 26.460 3.154 26.728 3.160 26.994 3.166 27.259 3.171 27.522 3.177 27.783 3.183 28.042 3.189 28.299 3.194 28.555 3.200 28.808 3.206 29.059 3.211 29.309 3.217 29.556 3.223 29.801 3.228 30.045 3.234 30.286 3.240 30.525 3.245 30.762 3.251 30.998 3.256 31.231 3.262 31.463 3.268 31.692 3.273 31.920 3.279 32.146 3.284 32.371 3.290 32.594 3.295 32.815 3.301 33.036 3.306 33.255 3.311 33.473 3.317 33.690 3.322 33.906 3.327 34.121 3.332 34.336 3.336 34.550 3.341 34.765 3.345 34.979 3.350 35.193 3.353 35.408 3.357 35.623 3.361 35.840 3.364 36.057 3.366 36.275 3.369 36.495 3.371 36.717 3.373 36.941 3.374 37.167 3.375 37.396 3.375 37.628 3.375 37.863 3.374 38.059 3.378 38.293 3.377 38.526 3.375 38.758 3.374 38.988 3.373 39.217 3.372 39.446 3.371 39.673 3.370 39.899 3.369 40.124 3.367 40.349 3.366 40.573 3.365 40.795 3.363 41.017 3.362 41.239 3.360 41.460 3.358 41.680 3.357 41.899 3.355 42.118 3.353 42.336 3.351 42.554 3.349 42.771 3.347 42.988 3.345 43.204 3.342 43.420 3.340 43.635 3.337 43.850 3.335 44.065 3.332 44.279 3.329 44.493 3.326 44.706 3.323 44.919 3.320 45.132 3.317 45.345 3.314 45.557 3.310 45.769 3.307 45.981 3.303 46.193 3.300 46.405 3.296 46.616 3.292 46.828 3.288 47.039 3.284 47.250 3.279 47.462 3.275 47.673 3.270 47.885 3.265 48.096 3.261 48.308 3.256 48.520 3.250 48.732 3.245 48.945 3.240 49.158 3.234 49.371 3.228 49.585 3.222 49.799 3.216 50.014 3.210 50.230 3.203 50.446 3.196 50.663 3.189 50.881 3.182 51.0992 3.175 51.3186 3.167 51.5389 3.159 51.7602 3.151 51.9825 3.143 52.2059 3.135 52.4304 3.126 52.6560 3.117 52.8828 3.108 53.1108 3.098 53.3401 3.088 53.5705 3.078 53.8023 3.068 54.0353 3.058 54.2695 3.047 54.5051 3.036 54.7420 3.025 54.9801 3.013 55.2195 3.001 55.4601 2.989 55.7020 2.977 55.9450 2.965 56.1893 2.952 56.4347 2.939 56.6812 2.926 56.9288 2.912 57.1774 2.898 57.4270 2.884 57.6776 2.870 57.9292 2.856 58.1817 2.841 58.4351 2.827 58.6893 2.812 58.9445 2.797 59.2006 2.781 59.4575 2.766 59.7154 2.750 59.9743 2.734 60.2342 2.717 60.4953 2.701 60.7577 2.684 61.0214 2.667 61.2868 2.650 61.5538 2.632 61.8228 2.614 62.0941 2.596 62.3679 2.577 62.6445 2.558 62.9244 2.539 63.2079 2.519 63.4954 2.498 63.7874 2.477 64.0845 2.455 64.3871 2.432 64.6960 2.409 65.0115 2.385 65.3345 2.360 65.6656 2.334 66.0053 2.306 66.3544 2.278 66.7135 2.249 67.083 2.218 67.464 2.186 67.857 2.152 68.262 2.117 68.679 2.081 69.110 2.043 69.553 2.004 70.009 1.963 70.477 1.921 70.957 1.878 71.448 1.833 71.948 1.787 72.455 1.740 72.967 1.693 73.481 1.645 73.994 1.597 74.500 1.550 74.995 1.504 75.471 1.460 75.922 1.418 76.338 1.380 76.710 1.346 77.026 1.318 77.272 1.297 77.356 1.290

FIG. 9 is a graph obtained by plotting the values of θi and sagY in Table 1. FIG. 12 is a graph showing a relationship between r/R and θi-θn. Here, r/R is a value obtained by normalizing, with respect to the outermost radius of the lens, the distance in the direction parallel to the light entrance surface 11 from the optical axis A to the arbitrary point on the light exit surface 12, where r is the distance in the direction parallel to the light entrance surface from the optical axis to the arbitrary point on the light exit surface, and R is the outermost radius of the lens (see FIG. 7).

θi-θn is an angle of a light ray emitted at an angle of θi, with respect to a normal line at a point on the light exit surface 12 reached by the light ray, that is, an incident angle of the light ray on the light exit surface 12. As a condition of the total reflection region 124 of the first light exit surface 121, since the refractive index of the transparent material constituting the lens in Example 1 is 1.492, θi -θn is 42.1 degrees or more. Accordingly, FIG. 12 shows that in Example 1, the transmissive region 123 of the first light exit surface 121 is a narrow region in the vicinity of the optical axis and the total reflection region 124 is a wide region away from the optical axis. FIG. 12 also shows that in Example 1, the entire second light exit surface 122 totally reflects the light emitted from the starting point Q.

In Example 1, R_(in), R_(out), R_(T), and R shown in FIG. 7 are 3.60, 5.85, 4.50, and 6.25, respectively. Accordingly, R_(in)/R is 0.58, R_(out)/R is 0.94, and (R_(out)+R_(T))/2R is 0.83, and these values satisfy the above inequalities (1) to (3).

Furthermore, in Example 1, h shown in FIG. 7 is 0.50. Therefore, tan⁻¹(h/(R_(out)−R_(T))) is 20.7 degrees, which satisfies the above inequality (4).

FIG. 15 shows the illuminance distribution on the surface to be irradiated obtained by calculation assuming that the lighting device of Example 1 (i.e., the illuminating lens in FIG. 9 and the light emitting diode) is used and the surface to be irradiated is placed at a distance of 16.4 mm from the light emitting diode. FIG. 18 shows the illuminance distribution on the surface to be irradiated obtained by calculation assuming that only the same light emitting diode as in FIG. 15 is used and the surface to be irradiated is placed at a distance of 16.4 mm from the light emitting diode. Each of FIG. 15 and FIG. 18 shows a curve indicating the distribution of illuminances on the surface to be irradiated when the illuminances are normalized with respect to the illuminance at the center of the optical axis being 1. A comparison between FIG. 15 and FIG. 18 shows that the illuminating lens is effective in increasing the illuminated area of the surface to be irradiated.

Example 2

Table 2 below shows specific numerical values in Example 2.

TABLE 2 θi sagY 0.000 1.592 0.773 1.594 1.539 1.600 2.294 1.610 3.032 1.624 3.750 1.640 4.445 1.659 5.116 1.681 5.761 1.705 6.381 1.730 6.975 1.757 7.546 1.785 8.094 1.814 8.619 1.844 9.125 1.874 9.611 1.905 10.079 1.935 10.531 1.966 10.967 1.997 11.389 2.028 11.798 2.059 12.196 2.089 12.582 2.119 12.958 2.149 13.325 2.179 13.684 2.208 14.034 2.236 14.378 2.264 14.715 2.292 15.047 2.319 15.373 2.346 15.694 2.372 16.011 2.398 16.324 2.423 16.633 2.447 16.939 2.471 17.242 2.494 17.542 2.517 17.840 2.539 18.136 2.560 18.430 2.581 18.723 2.601 19.014 2.620 19.303 2.639 19.592 2.658 19.880 2.676 20.166 2.693 20.452 2.710 20.738 2.726 21.022 2.741 21.307 2.756 21.590 2.771 21.874 2.785 22.157 2.798 22.440 2.811 22.723 2.824 23.005 2.836 23.288 2.847 23.570 2.858 23.852 2.869 24.133 2.879 24.415 2.889 24.696 2.899 24.977 2.908 25.258 2.917 25.538 2.925 25.818 2.933 26.097 2.941 26.376 2.948 26.655 2.955 26.933 2.962 27.210 2.969 27.486 2.975 27.762 2.982 28.037 2.988 28.311 2.993 28.584 2.999 28.856 3.004 29.127 3.010 29.397 3.015 29.666 3.020 29.933 3.025 30.199 3.029 30.464 3.034 30.727 3.038 30.988 3.043 31.248 3.047 31.506 3.052 31.763 3.056 32.018 3.060 32.271 3.064 32.523 3.068 32.772 3.073 33.020 3.077 33.266 3.081 33.510 3.085 33.753 3.089 33.993 3.093 34.232 3.097 34.469 3.101 34.704 3.104 34.938 3.108 35.170 3.112 35.400 3.116 35.629 3.120 35.857 3.124 36.083 3.127 36.308 3.131 36.532 3.134 36.754 3.138 36.976 3.141 37.197 3.144 37.418 3.147 37.638 3.150 37.858 3.153 38.078 3.156 38.298 3.158 38.519 3.160 38.740 3.162 38.962 3.164 39.185 3.165 39.410 3.166 39.636 3.167 39.865 3.167 40.095 3.166 40.329 3.166 40.566 3.164 40.818 3.161 41.067 3.158 41.315 3.155 41.560 3.152 41.804 3.150 42.045 3.147 42.285 3.144 42.523 3.141 42.760 3.139 42.995 3.136 43.229 3.133 43.462 3.131 43.693 3.128 43.923 3.125 44.152 3.123 44.381 3.120 44.609 3.117 44.836 3.114 45.062 3.111 45.288 3.108 45.513 3.104 45.738 3.101 45.963 3.098 46.188 3.094 46.412 3.090 46.637 3.086 46.862 3.082 47.086 3.078 47.311 3.074 47.537 3.069 47.762 3.065 47.988 3.060 48.215 3.055 48.442 3.050 48.669 3.044 48.897 3.039 49.126 3.033 49.355 3.027 49.585 3.021 49.816 3.014 50.048 3.008 50.280 3.001 50.514 2.994 50.748 2.987 50.983 2.979 51.218 2.971 51.455 2.963 51.693 2.955 51.931 2.947 52.171 2.938 52.412 2.929 52.653 2.920 52.895 2.911 53.139 2.902 53.383 2.892 53.628 2.882 53.8744 2.872 54.1216 2.861 54.3698 2.851 54.6189 2.840 54.8690 2.829 55.1200 2.818 55.3721 2.806 55.6251 2.794 55.8792 2.782 56.1342 2.770 56.3903 2.758 56.6474 2.745 56.9055 2.732 57.1648 2.719 57.4251 2.706 57.6865 2.693 57.9490 2.679 58.2128 2.665 58.4777 2.651 58.7439 2.636 59.0114 2.621 59.2802 2.606 59.5504 2.591 59.8221 2.575 60.0953 2.560 60.3701 2.544 60.6465 2.527 60.9247 2.510 61.2048 2.493 61.4868 2.476 61.7709 2.458 62.0572 2.441 62.3459 2.422 62.6371 2.403 62.9309 2.384 63.2277 2.365 63.5275 2.345 63.8307 2.324 64.1376 2.303 64.4484 2.282 64.7636 2.260 65.0834 2.237 65.4084 2.214 65.7391 2.190 66.0761 2.165 66.4200 2.140 66.7716 2.113 67.1317 2.086 67.5013 2.057 67.8814 2.027 68.2733 1.996 68.6783 1.964 69.0981 1.930 69.5344 1.894 69.9892 1.856 70.4648 1.816 70.9637 1.773 71.4888 1.728 72.0434 1.679 72.6310 1.627 73.2558 1.572 73.922 1.512 74.636 1.447 75.402 1.377 76.228 1.302 77.120 1.219 78.086 1.130 79.135 1.032 80.278 0.925 81.524 0.807 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

FIG. 10 is a graph obtained by plotting the values of θi and sagY in Table 2. FIG. 13 is a graph showing a relationship between r/R and θi-θn. r/R and θi-θn in FIG. 13 are the same as those in FIG. 12.

In Example 2, the lens is made of a material having a refractive index of 1.492, as in the case of Example 1 described above. Accordingly, as a condition of the total reflection region 124 of the first light exit surface 121, θi-θn is 42.1 degrees or more, as in the case of Example 1. Accordingly, FIG. 13 shows that in Example 2, the transmissive region 123 is as narrow as that of Example 1, and the total reflection region 124 is as wide as that of Example 1. FIG. 13 also shows that in Example 2, the entire second light exit surface 122 totally reflects the light emitted from the starting point Q.

In Example 2, R_(in), R_(out), R_(T), and R shown in FIG. 8 are 3.76, 5.17, 4.70, and 6.0, respectively. Accordingly, R_(in)/R is 0.63, R_(out)/R is 0.86, and (R_(out)+R_(T))/2R is 0.78, and these values satisfy the above inequalities (1) to (3).

Furthermore, in Example 2, h shown in FIG. 8 is 0.50. Therefore, tan⁻¹(h/(R_(out)−R_(T))) is 28.0 degrees, which satisfies the above inequality (5).

FIG. 16 shows the illuminance distribution on the surface to be irradiated obtained by calculation assuming that the lighting device of Example 2 (i.e., the illuminating lens in FIG. 10 and the light emitting diode) is used and the surface to be irradiated is placed at a distance of 16.4 mm from the light emitting diode. FIG. 16 shows a curve indicating the distribution of illuminances on the surface to be irradiated when the illuminances are normalized with respect to the illuminance at the center of the optical axis being 1, as in the case of FIG. 15. A comparison between FIG. 16 and FIG. 18 shows that the illuminating lens is effective in increasing the illuminated area of the surface to be irradiated.

Example 3

Table 3 below shows specific numerical values in Example 3.

TABLE 3 θi sagY 0.000 1.682 0.731 1.684 1.458 1.689 2.175 1.698 2.878 1.710 3.565 1.725 4.233 1.743 4.879 1.763 5.504 1.785 6.107 1.809 6.687 1.834 7.246 1.860 7.785 1.887 8.303 1.915 8.802 1.944 9.284 1.973 9.749 2.002 10.198 2.032 10.633 2.061 11.054 2.091 11.463 2.120 11.861 2.150 12.248 2.179 12.625 2.208 12.993 2.236 13.353 2.264 13.706 2.292 14.052 2.319 14.391 2.346 14.725 2.372 15.054 2.398 15.377 2.423 15.697 2.448 16.012 2.472 16.324 2.496 16.633 2.519 16.939 2.541 17.242 2.563 17.543 2.584 17.842 2.605 18.140 2.625 18.435 2.644 18.729 2.663 19.022 2.682 19.314 2.699 19.604 2.716 19.894 2.733 20.183 2.749 20.471 2.764 20.759 2.779 21.047 2.794 21.333 2.808 21.620 2.821 21.906 2.834 22.192 2.846 22.477 2.858 22.763 2.869 23.048 2.880 23.333 2.891 23.617 2.901 23.901 2.911 24.185 2.920 24.469 2.929 24.752 2.938 25.035 2.946 25.318 2.954 25.600 2.962 25.881 2.969 26.162 2.976 26.443 2.983 26.722 2.989 27.001 2.996 27.279 3.002 27.556 3.008 27.833 3.013 28.108 3.019 28.382 3.024 28.655 3.030 28.926 3.035 29.197 3.040 29.466 3.044 29.734 3.049 30.000 3.054 30.264 3.058 30.527 3.063 30.789 3.067 31.048 3.071 31.306 3.076 31.563 3.080 31.817 3.084 32.069 3.088 32.320 3.092 32.569 3.097 32.816 3.101 33.061 3.105 33.304 3.109 33.545 3.113 33.784 3.117 34.022 3.121 34.258 3.125 34.492 3.129 34.724 3.133 34.955 3.137 35.184 3.141 35.412 3.145 35.639 3.149 35.864 3.153 36.088 3.156 36.311 3.160 36.533 3.163 36.755 3.167 36.976 3.170 37.197 3.173 37.417 3.176 37.638 3.178 37.859 3.181 38.081 3.183 38.303 3.185 38.526 3.186 38.751 3.188 38.977 3.189 39.205 3.189 39.436 3.189 39.696 3.186 39.954 3.182 40.209 3.179 40.462 3.176 40.713 3.173 40.962 3.170 41.208 3.167 41.453 3.164 41.695 3.162 41.935 3.159 42.174 3.156 42.411 3.154 42.646 3.151 42.880 3.149 43.113 3.146 43.344 3.144 43.573 3.141 43.802 3.139 44.030 3.136 44.257 3.133 44.482 3.131 44.708 3.128 44.932 3.125 45.156 3.122 45.379 3.119 45.603 3.116 45.825 3.113 46.048 3.109 46.271 3.106 46.493 3.102 46.716 3.098 46.938 3.094 47.161 3.090 47.385 3.086 47.608 3.081 47.833 3.077 48.057 3.072 48.283 3.067 48.509 3.062 48.735 3.056 48.963 3.050 49.191 3.044 49.421 3.038 49.651 3.032 49.882 3.025 50.115 3.019 50.348 3.011 50.583 3.004 50.819 2.996 51.056 2.989 51.294 2.981 51.534 2.972 51.775 2.963 52.017 2.955 52.260 2.945 52.505 2.936 52.752 2.926 52.999 2.916 53.248 2.906 53.499 2.896 53.7507 2.885 54.0040 2.874 54.2586 2.862 54.5145 2.851 54.7719 2.839 55.0305 2.827 55.2905 2.815 55.5519 2.802 55.8145 2.789 56.0784 2.776 56.3436 2.763 56.6100 2.749 56.8777 2.735 57.1466 2.721 57.4166 2.707 57.6879 2.692 57.9603 2.678 58.2339 2.663 58.5086 2.647 58.7844 2.632 59.0615 2.616 59.3396 2.600 59.6190 2.584 59.8995 2.567 60.1813 2.551 60.4643 2.534 60.7487 2.517 61.0345 2.499 61.3217 2.481 61.6105 2.463 61.9009 2.445 62.1932 2.427 62.4875 2.408 62.7839 2.388 63.0826 2.369 63.3839 2.349 63.6880 2.328 63.9952 2.307 64.3059 2.286 64.6204 2.264 64.9391 2.242 65.2624 2.219 65.5910 2.195 65.9253 2.171 66.2659 2.146 66.6136 2.120 66.9690 2.093 67.3330 2.065 67.7065 2.036 68.0905 2.006 68.4860 1.975 68.8943 1.942 69.3166 1.908 69.7544 1.871 70.2091 1.834 70.6824 1.794 71.1762 1.752 71.6924 1.707 72.2332 1.660 72.8008 1.611 73.3979 1.558 74.027 1.502 74.691 1.442 75.394 1.378 76.138 1.310 76.927 1.238 77.766 1.161 78.658 1.078 79.609 0.990 80.622 0.895 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

FIG. 11 is a graph obtained by plotting the values of θi and sagY in Table 3. FIG. 14 is a graph showing a relationship between r/R and θi-θn. r/R and θi-θn in FIG. 14 are the same as those in FIG. 12.

In Example 3, the lens is made of a material having a refractive index of 1.492, as in the case of Example 1 described above. Accordingly, as a condition of the total reflection region 124 of the first light exit surface 121, θi-θn is 42.1 degrees or more, as in the case of Example 1. Accordingly, FIG. 14 shows that in Example 3, the transmissive region 123 is as narrow as that of Example 1, and the total reflection region 124 is as wide as that of Example 1. FIG. 14 also shows that in Example 3, the entire second light exit surface 122 totally reflects the light emitted from the starting point Q.

In Example 3, R_(in), R_(out), R_(T), and R shown in FIG. 8 are 3.84, 5.76, 4.80, and 6.0, respectively. Accordingly, R_(in)/R is 0.64, R_(out)/R is 0.96, and (R_(out)+R_(T))/2R is 0.88, and these values satisfy the above inequalities (1) to (3).

Furthermore, in Example 3, h shown in FIG. 8 is 0.50. Therefore, tan⁻¹(h/(R_(out)−R_(T))) is 27.5 degrees, which satisfies the above inequality (5).

FIG. 17 shows the illuminance distribution on the surface to be irradiated obtained by calculation assuming that the lighting device of Example 3 (i.e., the illuminating lens in FIG. 11 and the light emitting diode) is used and the surface to be irradiated is placed at a distance of 16.4 mm from the light emitting diode. FIG. 17 shows a curve indicating the distribution of illuminances on the surface to be irradiated when the illuminances are normalized with respect to the illuminance at the center of the optical axis being 1, as in the case of FIG. 15. A comparison between FIG. 17 and FIG. 18 shows that the illuminating lens is effective in increasing the illuminated area of the surface to be irradiated.

Third Embodiment

FIG. 19 is a schematic diagram of a surface light source 9 according to a third embodiment of the present invention. This surface light source 9 includes a plurality of lighting devices 7 of the second embodiment arranged in a plane, and a diffusing plate 4 disposed to cover the plurality of lighting devices 7. The lighting devices 7 may be arranged in a matrix as shown in FIG. 19. They may be arranged in a staggered manner.

The surface light source 9 includes a substrate 8 facing the diffusing plate 4 with the lighting devices 7 being disposed therebetween. As shown in FIG. 20, the light emitting diode 2 of each lighting device 7 is mounted on the substrate 8 via an interposer substrate 81. In the present embodiment, a reflecting plate 6 is disposed on the substrate 8 to cover the substrate 8 with the light emitting diodes 2 being exposed.

The lighting device 7 emits light to one surface 4 a of the diffusing plate 4. That is, the one surface 4 a of the diffusing plate 4 is the surface to be irradiated 3 that has been described in the first and second embodiments. The diffusing plate 4 emits the light received on its one surface 4 a from the other surface 4 b in a diffused manner. The lighting devices 7 emit light individually toward a large area of the one surface 4 a of the diffusing plate 4 so that the one surface 4 a has a uniform illuminance, and upon receiving this light, the diffusing plate 4 emits the light diffusely. As a result, the surface light source capable of emitting light having less uneven brightness in the plane is obtained.

The light emitted from the lighting device 7 is diffused by the diffusing plate 4 so that the diffuse light returns to the lighting device side or passes through the diffusing plate 4. The light that has returned to the lighting device side and struck the reflecting plate 6 is reflected at the reflecting plate 6 and again enters the diffusing plate 4.

FIG. 21 shows the illuminance distribution on the light entrance surface (one surface on the side of the lighting device) of the diffusing plate obtained by calculation assuming that five lighting devices of Example 1 each including the illuminating lens in FIG. 9 and the light emitting diode are arranged in a line at a pitch of 60 mm and the diffusing plate is placed at a distance of 16.4 mm from the light emitting diodes. Small fluctuations in the illuminance distribution are attributed to a small number of light rays to be evaluated in calculating the illuminances. FIG. 22 and FIG. 23 show the illuminance distribution obtained in the same manner when the lighting devices of Example 2 are used and the illuminance distribution obtained when the lighting devices of Example 3 are used, respectively.

FIG. 24 shows the illuminance distribution on the light entrance surface of the diffusing plate obtained by calculation assuming that five light emitting diodes only are arranged in a line with a pitch of 60 mm and the diffusing plate is placed at a distance of 16.4 mm from the light emitting diodes.

A comparison between FIGS. 21 to 23 and FIG. 24 shows that the illuminating lens is effective in illuminating the light entrance surface of the diffusing plate uniformly.

Fourth Embodiment

FIG. 25 is a schematic diagram of a liquid-crystal display apparatus according to a fourth embodiment of the present invention. This liquid-crystal display apparatus includes a liquid-crystal panel 5, and a surface light source 9 of the third embodiment disposed behind the liquid-crystal panel 5.

A plurality of lighting devices 7 each including the light emitting diode 2 and the illuminating lens 1 are arranged in a plane, and the diffusing plate 4 is illuminated by these lighting devices 7. The underside (one surface) of the diffusing plate 4 is irradiated with the light emitted from the lighting devices 7 to have a uniform illuminance, and then the light is diffused by the diffusing plate 4. Thus, the liquid-crystal panel 5 is illuminated by the diffused light.

It is preferable that an optical sheet such as a diffusing sheet or a prism sheet is disposed between the liquid-crystal panel 5 and the surface light source 9. In this case, the light that has passed through the diffusing plate 4 further is diffused by the optical sheet and illuminates the liquid-crystal panel 5.

The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this specification are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein. 

1. An illuminating lens for spreading light emitted from a light source so that a surface to be irradiated is irradiated with the spread light, the lens comprising: a light entrance surface through which the light emitted from the light source enters the lens; a light exit surface through which the light that has entered the lens exits the lens; and a bottom surface configured to surround the light entrance surface and to face oppositely to the light exit surface, wherein the light exit surface has a first light exit surface and a second light exit surface, the first light exit surface being recessed toward a point on an optical axis of the illuminating lens, and the second light exit surface extending outwardly from a periphery of the first light exit surface to form a convex, the first light exit surface has a transmissive region located in the center of the first light exit surface and a total reflection region located around the transmissive region, the transmissive region being capable of transmitting light that has been emitted from a starting point at a relatively small angle with respect to the optical axis and then reached the first light exit surface, when a position of the light source on the optical axis is defined as the starting point, and the total reflection region being capable of totally reflecting light that has been emitted from the starting point at a relatively large angle with respect to the optical axis and then reached the first light exit surface, the second light exit surface has a shape capable of transmitting approximately the entire amount of light that has been emitted from the starting point and then reached the second light exit surface, and of totally reflecting approximately the entire amount of the light that has been totally reflected at the total reflection region and then reached the second light exit surface, and the bottom surface is provided with a projecting portion or a recessed portion for reflecting light that has been emitted from the light source, totally reflected repeatedly at the light exit surface, and then reached the bottom surface, the projecting portion or the recessed portion having a pair of side surfaces that meet each other to form a ridge.
 2. The illuminating lens according to claim 1, wherein the light exit surface is axisymmetric with respect to the optical axis.
 3. The illuminating lens according to claim 1, wherein the projecting portion or the recessed portion has a ring shape with the optical axis being the center of the ring shape, and satisfies the following inequalities (1) to (3): 0.1<R _(in) /R<0.75  (1) 0.75<R _(out) /R  (2) 0.62<(R _(out) +R _(T))/2R<0.95  (3) where R_(in) is an internal radius of the projecting portion or the recessed portion, R_(out) is an outer radius of the projecting portion or the recessed portion, R_(T) is a distance between the optical axis and the ridge formed by the pair of side surfaces of the projecting portion or the recessed portion that meet each other, and R is an outermost radius of the illuminating lens.
 4. The illuminating lens according to claim 3, wherein the bottom surface is flat, and the projecting portion is formed on the bottom surface, and the projecting portion satisfies the following inequality (4): 5.0 degrees<tan⁻¹(h/(R _(out) −R _(T)))<50.0 degrees  (4) where h is a height from the bottom surface to the ridge formed by the pair of side surface of the projecting portion that meet each other.
 5. The illuminating lens according to claim 3, wherein the bottom surface is flat, and the recessed portion is formed on the bottom surface, and the recessed portion satisfies the following inequality (5): 15.0 degrees<tan⁻¹(h/(R _(out) −R _(T)))<30.0 degrees  (5) where h is a depth from the bottom surface to the ridge formed by the pair of side surface of the recessed portion that meet each other.
 6. The illuminating lens according to claim 1, wherein the pair of side surface are both tapered surfaces.
 7. The illuminating lens according to claim 1, wherein the entire second light exit surface transmits the light that has been emitted from the starting point.
 8. The illuminating lens according to claim 1, wherein the second light exit surface totally reflects a part of the light that has been emitted from the starting point and transmits the remaining part of the light.
 9. A lighting device comprising: a light emitting diode for emitting light; and an illuminating lens for spreading light emitted from the light emitting diode so that a surface to be irradiated is irradiated with the spread light, wherein the illuminating lens is the illuminating lens according to claim
 1. 10. A surface light source comprising: a plurality of lighting devices arranged in a plane; and a diffusing plate disposed to cover the plurality of lighting devices, the diffusing plate being configured to receive on one surface thereof light emitted from the plurality of lighting devices and to emit the light from the other surface thereof in a diffused manner, wherein each of the plurality of lighting devices is the lighting device according to claim
 9. 11. The surface light source according to claim 10, further comprising: a substrate on which the light emitting diode included in each of the plurality of lighting devices is mounted, the substrate facing the diffusing plate with the plurality of lighting devices being disposed therebetween; and a reflecting plate disposed on the substrate to cover the substrate with the light emitting diodes being exposed.
 12. A liquid-crystal display apparatus comprising: a liquid-crystal panel; and the surface light source according to claim 10 disposed behind the liquid-crystal panel. 